The differential maturation of two processing rates related to digit span

Recent studies have proposed that rapid-speaking durations predict short-term memory spans. However, N. Cowan et al. (1998, Journal of Experimental Psychology: General, 127, 141-160) found two separate types of processing durations related to digit span for children in Grade 1 (7-8 years), Grade 3 (9-10 years), and Grade 5 (11-12 years): rapid-speaking durations (thought to index the rate of covert articulation) and the durations of interword pauses in the memory span task responses (thought to index the rate of short-term memory retrieval). The present analysis additionally establishes the differential maturation of those two durations. Within-age correlations between span and rapid-speaking durations were significant only in first graders; correlations between span and interword pauses, only in fifth graders. When subsamples were selected to match spans across age groups, both types of duration also were matched between Grades 1 and 3. However, fifth graders had considerably shorter interword pauses than their third-grade counterparts. Thus, a particular memory span is accompanied by different profiles of processing rates in children of different ages.